Re: Overloading mathematica built in functions

*To*: mathgroup at smc.vnet.net*Subject*: [mg5750] Re: [mg5716] Overloading mathematica built in functions*From*: BobHanlon at aol.com*Date*: Tue, 14 Jan 1997 10:42:28 -0500*Sender*: owner-wri-mathgroup at wolfram.com

Playing with built-in definitions is risky. There may be unintentional side effects. Recommend defining a new function. Bob Hanlon _______________ mySum[x_List] := Plus @@ x; mySum[expr_, {iterator__}] := Sum[expr, {iterator}]; theList = Array[x, {3}] {x[1], x[2], x[3]} mySum[theList] x[1] + x[2] + x[3] mySum[n^2, {5}] 2 5 n mySum[n^2, {n, 5}] 55 mySum[n^2, {n, 1, 5}] 55 mySum[n^2, {n, 1, 5, 1}] 55 --------------------- Forwarded message: From: seanross at worldnet.att.net To: mathgroup at smc.vnet.net To: mathgroup at smc.vnet.net I want to add a capability to the Sum function. If I give it a single argument that is a 1-D list, I want it to sum the list. For example: In[1]:= w={1,1,1,3}; Sum[w] Out[1]:= 5 The function sum[f_List]:=Sum[f[[i]],{i,1,Length[f]}]; performs this function, However Unprotect[Sum]; Sum[f_List]:=Sum[f[[i]],{i,1,Length[f]}]; Protect[Sum]; does not work. Does anyone know why? I am guessing it has something to do with the attribute HoldAll on the built-in function Sum. Is there a way to overload a function so that the attributes are different for different argument lists? Thanks